The Manchester United boss was delighted to secure three points against rivals City at the Etihad Stadium but pointed out it is still very early in the title race.
In a dramatic derby clash, United raced into a two-goal lead thanks to a first-half double from Wayne Rooney. The champions launched a strong comeback after the break as Yaya Toure and Pablo Zabaleta strikes got them back on level terms. There was a final twist in the tale, though, when Robin van Persie curled home a stoppage-time free kick to give the visitors all three points, which takes them six clear at the top of the table.
"It is too early to draw any conclusions about the title race," Ferguson told Sky Sports. "City will be fresh for the second half of the season – they are out of European football - but we will still have Europe, the FA Cup and the league to contend with. That means we will have a real challenge but we have always accepted these challenges.
"This doesn’t make up for last year’s derby defeats yet. There is still a long way to go this season, but I’ve not known many more dramatic days than that in the past. We’ve done it before against City of course, but today was a special one simply because they haven’t lost at home for two years and both of us are contesting with each other at the top of the league.
"It was a fantastic game; you couldn’t take your eyes off it. I absolutely thought we were worthy winners. We played very well and should have finished the game off before we did."
Sir Alex was unhappy with the decision to rule out an Ashley Young goal for offside with the score at 2-0, which he felt was a key turning point in the match, and the incident that prompted City’s recovery in the second half.
"We should have been 3-0 up after scoring a goal that was perfectly onside and then they go up the park and score," he said. "Football is a funny game. That’s the sort of moments in a match that can kill you and football can kick you in the teeth in that way.
"After that goal they scored a second one and at that point they deserved it. They had come back into the game, were fighting like hell and gambled everything with three strikers on. But up until that first goal I thought we were far better than them."
The United boss was delighted with the performance of match-winner Van Persie and seemed even more satisfied with the improvement his side showed in comparison to last season’s crucial derby defeat at the Etihad Stadium, where a tame 1-0 loss eventually cost them the league.
"The free kick has taken a deflection but it is an exceptional hit. Van Persie’s overall game today was absolutely terrific; he kept them on the back foot for the whole match really," Ferguson said. "I think we can be proud of the fact that opposed to what we did last year where we stood off too much and gave them far too much respect, there was a much better team spirit about us and the players were determined to win the match."